1. Field of the Invention
The field of the invention relates to security inspection systems generally, and more particularly, to a security inspection system having: an apparatus configured to asymmetrically balance a magnetic field generated by an inductive sensor; an apparatus configured to minimize vulnerability to electromagnetic interference caused by random geometrical arrangements of relays and capacitors used to operate the inductive sensor; an apparatus configured to protect magnetic fields generated by the inductive sensor from external electrical interference; and an apparatus for detecting shanks in shoes worn by an inspected person.
2. Discussion of Related Art
Extant security inspection systems use known technologies such as nuclear magnetic resonance (NMR), nuclear quadrupolar resonance (NQR), metal detection, and x-rays, among others, to detect weapons, explosives, illegal drugs, and other kinds of substances of interest in and/or on an item, such as shoes, luggage, clothing, and the like.
When security is heightened, persons to be scanned are often required to remove their shoes. The shoes are then typically placed in plastic tubs that move, via a conveyor belt, into an x-ray scanner. Additionally, or alternatively, security personnel may visually inspect the shoes, swab the interior and/or exterior of the shoes for trace detection purposes, and/or pass a hand-held metal detector over the shoes. Such methods consume time, inconvenience passengers, and slow the rate of a security checkpoint's throughput. A need therefore exists for a solution that enables simple and accurate detection of weapons, explosives, drugs, and/or other substances of interest that may be hidden in a person's shoes while the shoes are being worn. Another need exists for a solution that provides simple and accurate detection of weapons, explosives, illegal drugs, and/or other substances of interest that may be hidden, alternatively or additionally, in the person's socks and/or clothing present on the person's lower extremities while such socks and/or clothing are being worn.
Various devices have been developed in attempts to provide solutions to one or more of these needs. One example of such a device is a walkthrough NQR shoe scanner that positions a NQR sensor in the floor of the shoe scanner and flanks the NQR sensor with two opposing vertical side walls that are electrically connected to the floor of the shoe scanner. A channel formed by the space between the opposing vertical side walls extends the length of the shoe scanner so that a person can enter one (open) end of the shoe scanner and exit the opposite (open) end. As the person stands in the central portion of the NQR shoe scanner, the NQR sensor operates to detect alarm objects (e.g., weapons, explosives, illegal drugs, etc.) in or on the person's shoes, socks, or articles of clothing.
Another example is a passenger screening system that positions an inductive NQR sensor in a floor of the passenger screening system and flanks the inductive NQR sensor with three vertical, electrically conductive walls that are joined together and attached to the floor of the passenger screening system. The three vertical, electrically conductive walls include two electrically conductive and opposing side walls and one electrically conductive end wall. A channel formed by the space between the opposing side walls extends from an open end of the passenger screening system to the end wall that forms the opposite end of the passenger screening system so that a person can enter and exit the passenger screening system only from the open end of the channel. The passenger screening system also includes a metal detection sensor having two metal detector conductive traces—a first metal detector conductive trace positioned on one of the opposing side walls; and a second metal detector conductive trace positioned on the other of the opposing side walls. The metal detector conductive traces are configured to generate a uniform magnetic field when no metallic object or substance is present within the scanning area. Any metallic object or substance that is later positioned within the scanning area will disturb the otherwise balanced magnetic field generated by the metal detection conductive traces. This disturbance creates an electrical and/or magnetic imbalance between the metal detector conductive traces, which causes the passenger screening system to receive a signal indicating that a metallic object has been detected within the scanning area.
Known security inspection systems, such as the walkthrough NQR shoe scanner and the passenger screening system, illustratively described above, have several disadvantages. Principal among them is that the magnetic field becomes imbalanced when the channel is capped by a kiosk and/or an end wall. Additionally, the magnetic field degrades if not effectively shielded from at least the electric component of internal and/or external electromagnetic fields. Thus, in addition to these needs referenced above, a need exists for a shoe scanner that asymmetrically balances a magnetic field generated by an inductive sensor. A need also exists for a shoe scanner that shields the magnetic field from vulnerability to electromagnetic interference caused by random geometrical arrangements of relays and capacitors used to operate the inductive sensor. An additional need exists for an asymmetric, electrically shielded shoe scanner configured to simply and accurately detect the presence of a metallic shoe shank in shoes worn by an inspected person.